1. Field of the Invention
Embodiments described herein relate generally to a multi charged particle beam writing apparatus and a multi charged particle beam writing method, and for example, a method for making a plurality of irradiation positions by multi-beams with high precision.
2. Related Art
A lithography technique that is charge in the progress of refinement of a semiconductor device is a very important process to generate a unique pattern in a semiconductor fabricating process. In recent years, with high integration of LSI, a line width of a circuit required for the semiconductor device has been refined every year. Herein, an electron ray (electron beam) writing technique intrinsically has excellent resolution and a pattern is written on a wafer and the like by using an electron ray.
For example, a writing apparatus using multi-beams is used. As compared with a case of writing the pattern by using one electron beam, since a lot of beams may be irradiated once by using the multi-beams, throughput may be significantly improved. In the multi-beam type writing apparatus, for example, an electron beam emitted from an electron gun passes through a mask having a plurality of holes to form the multi-beams, the multi-beams are blanking-controlled, and each beam which is not shielded is reduced in size by using an optical system, and is deflected by using a deflector to be irradiated to a desired point on a target object (see Published Unexamined Japanese Patent Application No. 2006-261342 (JP-A-2006-261342), for example).
In the multi-beam type writing apparatus, the plurality of beams are irradiated at a time and irradiation positions of the plurality of beams are required to be adjusted with high precision. However, a field is principally deformed in the optical system.
FIGS. 16A and 16B are conceptual diagrams for describing one example of the field deformation. Multi-beams 301A to 301H irradiated at a time, which are formed by passing through a plurality of holes A to H of the mask placed at a predetermined pitch will be irradiated on the surface of a target object 300 at a predetermined interval k, as illustrated in FIG. 16A. However, intervals k1 to k7 of the beams depend on a place as illustrated in FIG. 16B due to the aforementioned deformation in the optical system or deviation in placement position of the intervals of the holes to form the multi-beams or the like. When a pattern is formed while the deformation occurs, an error occurs in the shape of the formed pattern and it is difficult to write the pattern with high precision. In order to correct the deformation, as fabrication precision, in order to adjust the fabrication precision to precision of for example, nm or less (for example, 0.1 nm), a significantly close design is required, which is not also realistic. In designing the optical system, even though the optical system may be designed with high precision, setting ranges of other design parameters are limited. As a result, when field deformation intends to be modified, optimization of these other conditions (for example, resolution performance, focal depth, and the like) may be interfered. When equalization of a magnetic field intends to be promoted in order to reduce deformation, for example, a huge lens barrel is required. A lot of complicated correction mechanisms are required in order to reduce deformation and an excessive burden is applied to the apparatus. After the writing apparatus is manufactured, adjustment to an actual apparatus is required, but although deformation intends to be modified, parameters of writing are complicatedly related to each other, and thus a parameter for modifying the deformation is not an independent variable. Therefore, optimization is difficult or enormous amount of time is required although the optimization may be achieved.
As described above, in the multi-beam type writing apparatus, the plurality of beams are irradiated at a time and irradiation positions of the plurality of beams are required to be adjusted with high precision. In the multi-beam type, the beams are shot by a raster scan scheme at a control grid interval while a stage moves, and beams having passed through different molding holes are connected to each other to form a pattern having a desired figure shape. However, a shot interval is increased due to the deformation in the optical system or the like. When the shot interval is decreased, the error occurs in the shape of the formed pattern and it is difficult to write the pattern with high precision.
FIG. 17 is a conceptual diagram illustrating one example of a case in which the shot interval is wider than the control grid interval due to the deformation. When the multi-beams A to H formed by passing through the plurality of holes A to H are used and filled at the control grid interval, the beams of the respective shots are ideally aligned at the control grid interval. However, when the shot intervals among the multi-beams irradiated at a time are increased due to the deformation from the first, each shot interval is wider than the control grid interval even when the shot is filled with the multi-beams at the control grid interval. If this goes on, the deviation (error) occurs in the shape or size of the formed pattern.